Considerable work has therefore been done in order to stabilize the support with regard to these support rehydration and/or redissolution processes.                It is thus taught in patent WO-99/42,214 that the introduction of elements selected from among: Si, Zr, Cu, Zn, Mn, Ba, Co, Ni, La allows to substantially limit the support rehydration/dissolution process in acid or neutral aqueous media.        
A preferred way of modifying the support consists in grafting at the surface of said support organic Si compounds of TEOS (TetraEthylOrthoSilicate) or TMOS (TriMethOxySilane) type.                Patent WO-02/07,883 teaches that modification of a Fischer-Tropsch synthesis catalyst support by impregnation of an organometallic compound of formula Me(OR)x with x ranging from 1 to 5, Me being a metal selected from among the following elements: Si, Zr, Cu, Zn, Mn, Ba, Co, Ni, Na, K, Ca, Sn, Cr, Fe, Li, Tl, Mg, Sr, Ga, Sb, A, Hf, Th, Ce, Ge, U, Nb, Ta, W, and R designating an alkyl or acyl group, allows to limit the formation of crystallized phases responsible for the activity loss of the catalyst under the operating conditions of the Fischer-Tropsch synthesis.        
The organometallic compound can possibly be decomposed by calcination after deposition of the active phase by impregnation. The major drawback of this preparation mode is the use of an organic solvent intended to solubilize the organometallic compound prior to the deposition thereof by impregnation.                Patents U.S. Pat. No. 5,169,821 and U.S. Pat. No. 5,397,806 teach that the introduction of silicon, zirconium or tantalum in a cobalt-based catalyst supported on titanium oxide of anatase type should allow to obtain a stabilizing effect towards a high-temperature regenerative treatment.        Mechanical stabilization towards the severe attrition conditions that prevail when using a slurry can also be obtained by adding silica (SiO2) and alumina (Al2O3) to an initial titanium oxide (TiO2) phase as described in patent WO-99/39,825.        The use of phases of spinel structure MAl2O4 in catalysis (hydrocarbon steam reforming, partial oxidation, water dealkylation) is generally justified by the particular surface properties of these solids, and their excellent textural and mechanical stability in the high temperature range required for these applications (for example in methane reforming for the production of synthesis gas as described by Xu Z, Li Y, Zhang J, Chang L, Zhou R, Duan Z in Applied Catal A General, (2001), 213(1), 65-71.        
Simple (AB2O4) or mixed (AxA′1−xB2O4) spinels are synthesized by bringing metal oxide mixtures obtained by coprecipitation of metallic precursors to high temperature.                In Fischer-Tropsch synthesis, the use of simple spinel type supports is described by Kondo S, Muraki H, Fujitanii Y in Sekiyu Gakkaishi (1984) 27 (6), 556-563. The use of MgAl2O4 allows to obtain, under test conditions (fixed bed), more active catalysts than on various transition aluminas (γ, δ, α).        
The presence of silicon, notably in silica-alumina form, in the support is however not mentioned by any of these authors.